In recent years, a communication network that communicably connects a plurality of information processing terminals or the like to each other becomes popular. In such a communication network, a plurality of information processing terminals share a communication bandwidth of the communication network with each other.
In a communication network where a common communication bandwidth is shared, the available communication bandwidth means a free bandwidth calculated by subtracting from the physical bandwidth of a bottleneck link on a communication network (communication line), other traffic flowing through the network. The available communication bandwidth may be referred to as an “available bandwidth” hereinafter. Other traffic flowing through the network may be referred to as “cross traffic” hereinafter. When, for example, the physical bandwidth of a bottleneck link on a communication network is “100” Mbps (megabits per sec) and the cross traffic is “30” Mbps, the available bandwidth is “100−30=70” Mbps.
It is important to know an available bandwidth for a communication network, for example, when pieces of information such as sounds and images are transmitted each other in real time among terminals, or when a specific transaction is executed within a predetermined period of time by transmitting and receiving data.
For example, in an application such as video chat or videoconference in which data including video images and sounds is bidirectionally exchanged between terminals, it is possible to prevent data loss by controlling the transmission rate of video images and sounds within the range of known available bandwidth. A technologies technology for estimating an available bandwidth of a communication network and controlling data transmission and reception in accordance with the available bandwidth, becomes more important.
As technologies related to bandwidth estimation on a communication network, the following patent literatures, for example, are disclosed.
PTL 1 discloses a technology related to a network bandwidth measuring system, which estimates an available bandwidth of a communication network between a transmission apparatus and a reception apparatus. In the technology disclosed in PTL 1, the transmitting-side apparatus transmits a plurality of measurement packets (packet trains) arranged in ascending or descending order of size, to the receiving-side apparatus at a specific transmission interval. The receiving-side apparatus compares the transmission intervals of the measurement packets with their reception intervals. The receiving-side apparatus estimates an available bandwidth by using a largest measurement packet among measurement packets having equal transmission and reception intervals.
PTL 2 discloses a method for measuring an available bandwidth of a communication network. With the technology disclosed in PTL 2, a measuring-side communication apparatus transmits a plurality of measurement packets to a receiving-side apparatus at a specific transmission rate. The measuring-side communication apparatus receives the reception times of the plurality of measurement packets. Based on the reception time of each packet, the measuring-side communication apparatus measures a time difference of transmission delay occurring between the measurement packets, and examines a trend of change of the time difference. When the time difference increases or decreases, the measuring-side communication apparatus changes the transmission rate and executes measurement and examination again. The measuring-side communication apparatus estimates an available bandwidth using the transmission rate when the time difference falls within a stable range.
PTL 3 discloses a technology related to a method for measuring an available bandwidth of a communication network. The technology disclosed in PTL 3 is used to determine the order of transmission destination of measurement packet trains, for each of a plurality of communication apparatuses connected to each other via a communication network. Each communication apparatus transmits the measurement packet trains in accordance with the determined order. In the technology disclosed in PTL 3, the order of transmission of measurement packets is determined so as not to simultaneously transmit measurement packets from a plurality of communication apparatuses to a particular communication apparatus.
As technologies related to bandwidth control on a communication network, the following patent literatures, for example, are available.
PTL 4 discloses a technology for bandwidth control on a communication network in delivering stream data from a particular root (delivery source) terminal to other terminals. The technology disclosed in PTL 4 is used to allocate part of an upload link bandwidth measured for each terminal to deliver stream data, and allocates the remainder of the upload link bandwidth to deliver data associated with the stream data.
PTL 5 discloses a technology related to a network switch, which controls a storm (abnormal transmission) of broadcast packets. With the technology disclosed in PTL 5, the network switch measures broadcast packets and other normal packets, which occupy traffic on a communication network. The network switch analyzes a bandwidth occupying rate of broadcast packets at which the broadcast packets have no influence on other normal packets, based on the measurement result. The network switch calculates a threshold used as a criterion for a stream (abnormal transmission) on the basis of the analysis result, and adjusts the amount of communication of broadcast packets on the basis of the threshold. PTL 6 discloses a technology for adjusting the streaming quality of the digital content based on the estimation result of an available bandwidth. PTL 7 discloses a technology for allocating a communication bandwidth requested by one subscriber apparatus to a communication channel that is not used by another subscriber apparatus, in a network that allows a plurality of subscriber apparatuses to share a bandwidth with each other.